I was making payments on a semi truck I bought two years ago but I decide this year pay it off, can I deduct this amount in my taxes

[kmolines]

The amount of payoff was $17000

[Critter]

No ... only the interest paid is a deductible expense on the tax return.  The principle portion of the payment is covered  by depreciating the asset per the IRS prescribed methods ...  a semi truck is depreciated over 3 years ( on 4 tax returns) so if you have not been depreciating it you need to do so now and amend the prior year returns as well. 

[SweetieJean]

According to the ProSeries depreciation listing, tractor = 3YR; trailer = 5YR.

[Critter]

Correct the tractor portion is 3 years and the trailer is 5 years as they are separate assets ... the OP said semi truck so I went with tractor since that is synonymous in trucker lingo.